Method of Manufacturing a Semiconductor Device by Plasma Doping

ABSTRACT

A method of manufacturing a semiconductor device includes forming a superjunction field effect transistor by: forming trenches in a semiconductor body from a first side: forming charge compensation layers by doping parts of the semiconductor body via sidewalls of the trenches by introducing dopants by plasma doping; after forming the charge compensation layers, widening a profile of the dopants introduced by plasma doping by diffusion caused by a thermal heating process; and forming a drain contact at a second side opposite to the first side. A surface concentration of the dopants introduced by plasma doping via a unit area of the sidewalls is at least five times larger than a concentration of dopants in a mesa region of the semiconductor body between neighboring trenches which corresponds to N, wherein N is a net doping of the semiconductor body between the neighboring trenches.

BACKGROUND

A key component in semiconductor applications is a solid state switch.As an example, switches turn loads of automotive applications orindustrial applications on and off. Solid state switches typicallyinclude, for example, field effect transistors (FETs) likemetal-oxide-semiconductor FETs (MOSFETs) or insulated gate bipolartransistors (IGBTs).

Key demands on solid state switches are low on-state resistance (Ron)and high breakdown voltage (Vbr). Minimizing the on-state resistance isoften at the expense of the breakdown voltage. Therefore, a trade-offbetween Ron and Vbr has to be met.

Superjunction structures are widely used to improve a trade-off betweenthe on-state resistance and the breakdown voltage. In a conventionaln-channel superjunction device, alternating n-doped and p-doped regionsreplace one comparatively lower n-doped drift zone. In an on-state,current flows through the n-doped regions of the superjunction devicewhich lowers the Ron. In an off or blocking state, the p-doped regionsand the n-doped regions deplete or compensate each other to provide ahigh Vbr. A compensation structure design is one key element forimproving the trade-off between Ron and Vbr.

Accordingly, a method of manufacturing a superjunction device and asuperjunction device with an improved compensation structure design isneeded.

SUMMARY

According to an embodiment of a method of manufacturing a semiconductordevice, the method includes forming a trench in a semiconductor body.The method further includes doping a part of the semiconductor body viasidewalls of the trench by plasma doping.

According to an embodiment of a semiconductor device, the semiconductordevice includes a first semiconductor region of a first conductivitytype at a sidewall of a trench extending into a semiconductor body froma first side. The semiconductor body further includes a drift zone ofthe first conductivity type. The semiconductor device further includes afirst semiconductor layer over the first semiconductor region in thetrench. The first semiconductor layer is of a second conductivity typecomplementary to the first conductivity type. The first conductivitytype of the first semiconductor region is determined by a first speciesof dopants in the first semiconductor region. A doping profile of thefirst species of dopants declines from a maximum in the firstsemiconductor region to a minimum or to a minimum doping plateau in thedrift zone. A value of the doping at the maximum is at least a factor of10 higher than the doping at the minimum or at the minimum dopingplateau.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of the specification. The drawings illustrateembodiments of the present invention and together with the descriptionserve to explain principles of the invention. Other embodiments of theinvention and many of the intended advantages will be readilyappreciated as they become better understood by reference to thefollowing detailed description. The elements of the drawings are notnecessarily to scale relative to each other. Like reference numeralsdesignate corresponding similar parts.

FIG. 1 is a schematic process chart of one embodiment of a method ofmanufacturing a semiconductor device according to an embodiment.

FIGS. 2A to 2F are cross-sectional views of a semiconductor body atdifferent process phases during one embodiment of a method ofmanufacturing a superjunction device.

FIGS. 3A to 3F illustrate schematic cross-sectional views of asemiconductor body at different process phases during another embodimentof a method of manufacturing a superjunction device.

FIG. 3G is a schematic illustration of profiles of p-doping and n-dopingalong a line A-A of FIG. 3F.

FIGS. 4A to 4J illustrate schematic cross-sectional views of asemiconductor body at different phases during yet another embodiment ofa method of manufacturing a superjunction device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top”,“bottom”, “front”, “back”, “leading”, “trailing”, “over”, “above”,“below”, etc., is used with reference to the orientation of theFigure(s) being described. Because components of the embodiments can bepositioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. For example, features illustrated ordescribed as part of one embodiment can be used on or in conjunctionwith other embodiments to yield yet a further embodiment. It is intendedthat the present invention includes such modifications and variations.The examples are described using specific language which should not beconstrued as limiting the scope of the appending claims. The drawingsare not scaled and are for illustrative purposes only. For clarity, thesame elements or manufacturing processes have been designated by thesame references in the different drawings if not stated otherwise.

The terms “lateral” and “horizontal” as used in this specificationintends to describe an orientation parallel to a first surface of asemiconductor substrate or semiconductor body. This can be for instancethe surface of a wafer or a die.

The term “vertical” as used in this specification intends to describe anorientation which is arranged perpendicular to the first surface of thesemiconductor substrate or semiconductor body.

As employed in this specification, the terms “coupled” and/or“electrically coupled” are not meant to mean that the elements must bedirectly coupled together—intervening elements may be provided betweenthe “coupled” or “electrically coupled” elements. The term “electricallyconnected” intends to describe a low-ohmic electric connection betweenthe elements electrically connected together.

In this specification, n-doped may refer to a first conductivity typewhile p-doped is referred to a second conductivity type. It goes withoutsaying that the semiconductor devices can be formed with opposite dopingrelations so that the first conductivity type can be p-doped and thesecond conductivity type can be n-doped. Furthermore, some Figuresillustrate relative doping concentrations by indicating “−” or “+” nextto the doping type. For example, “n⁻” means a doping concentration whichis less than the doping concentration of an “n”-doping region while an“n⁺”-doping region has a larger doping concentration than the “n”-dopingregion, Indicating the relative doping concentration does not, however,mean that doping regions of the same relative doping concentration havethe some absolute doping concentration unless otherwise stated. Forexample, two different n⁺ regions can have different absolute dopingconcentrations. The same applies, for example, to an n⁺ and a p⁺ region.

Specific embodiments described in this specification pertain to, withoutbeing limited thereto, power semiconductor devices which are controlledby field-effect and particularly to unipolar devices such as MOSFETs.

The term “field-effect” as used in this specification intends todescribe the electric field mediated formation of an “inversion channel”and/or control of conductivity and/or shape of the inversion channel ina semiconductor channel region.

In the context of the present specification, the term “MOS”(metal-oxide-semiconductor) should be understood as including the moregeneral term “MIS” (metal-insulator-semiconductor). For example, theterm MOSFET (metal-oxide-semiconductor field-effect transistor) shouldbe understood to include FETs having a gate insulator that is not anoxide, i.e., the term MOSFET is used in the more general term meaningIGFET (insulated-gate field-effect transistor) and MISFET, respectively.

FIG. 1 illustrates a schematic process chart of a method ofmanufacturing a semiconductor device. The method includes forming atrench in a semiconductor body (S100) and doping a part of thesemiconductor body via sidewalls of the trench by plasma doping (S110).

The semiconductor body may be a pre-processed single-crystallinesemiconductor substrate, for example a single-crystalline siliconsubstrate (Si substrate), a SiC substrate, a GaN substrate, a GaAssubstrate or a silicon-on-insulator substrate. The semiconductor bodymay include none, one or a plurality of doped and/or undoped layers onthe single-crystalline semiconductor substrate, e.g. epitaxialsemiconductor layers. As an example, a thickness of the semiconductorlayer(s) formed on the single-crystalline semiconductor substrate aswell as a doping of the one or several layers may be appropriatelychosen with regard to a desired voltage blocking capability of thesemiconductor device that is to be formed in the semiconductor body. Inparticular the doping level of the semiconductor body should be chosenin such a way that the charge balance of the final compensation deviceis adequate for a desired blocking behavior.

The trench may be formed by an appropriate process, e.g. dry and/or wetetching As an example, the trench may be formed in a silicon body by ananisotropic plasma etch process, e.g. reactive ion etching (RIE) usingan appropriate etch gas, e.g. at least one of Cl₂, Br₂, CCl₄, CHCl₃,CHBr₃, BCl₃, HBr. According to an embodiment, sidewalls of the trenchmay be slightly tapered, e.g. including a taper angle between 88° and90°. Slightly tapered trench sidewalls may be beneficial with regard toavoiding trench cavities when filling up trenches.

Plasma doping of the part of the semiconductor body via sidewalls of thetrench allows high dose implants at low energies and is also known asPLAD (plasma doping) or PIII (plasma immersion ion implantation). Thesemethods allow for a precise doping of the part of the semiconductor bodyat the trench sidewalls. A conformal doping of the part of thesemiconductor body at the trench sidewalls can be achieved by applying avoltage to a substrate surrounded by a radio frequency (RF) plasmaincluding a dopant gas. Collisions between ions and neutral atoms aswell as the biasing of the substrate lead to a broad annulardistribution of the dopants allowing for a homogeneous doping over thetrench sidewalls. Also a small vertical gradient in dose of doping inthe part of the semiconductor body may be achieved by plasma doping.This allows for a vertical variation of a degree of charge compensationimproving stability of manufacture and/or avalanche robustness. Avertical variation of dose of doping may be smaller 20%, or smaller than10% or smaller than 5%.

When doping with PLAD, the semiconductor substrate, e.g. a semiconductorwafer, is exposed to a plasma including ions of dopants. These ions areaccelerated by an electric field towards the substrate and are implantedinto an exposed surface of the substrate. An implanted dose can beadjusted or controlled via DC voltage pulses, e.g. negative voltagepulses. A Faraday system allows to adjust or control the dose. Two setsof coils, i.e. a horizontal coil and a vertical coil allow to generatethe plasma and keep it homogeneous. An ion density can be adjusted via adistance between the coils and the substrate. Interaction between thevertical coils and the horizontal coils allows to adjust or controlhomogeneity and the ion density.

A penetration depth of the dopants into the semiconductor body and theimplant dose may be adjusted via a pulsed DC voltage applied between thesemiconductor substrate and a shield ring surrounding it.

According to an embodiment, doping the part of the semiconductor body byplasma doping includes introducing the dopants into the part of thesemiconductor body via the sidewalls at a dose in a range of 5×10¹¹ cm⁻²to 5×10¹² m⁻², or in a range of 7×10¹¹ cm⁻² to 2×10¹² cm⁻². Thiscomparatively low dose requires modifications of the pulsed DC voltagetypically used. Typically doses exceeding 10¹⁵ cm⁻² implanted by thesetechniques. According to an embodiment, a pulse distance of the DCvoltage pulses is adjusted in a range of 100 μs to 10 ms, in particularbetween 500 μs and 5 ms. A DC voltage pulse rise time is set to a valuesmaller than 0.1 μs, for example. According to an embodiment a pulsewidth ranges between 0.5 μs to 20 μs, or between 1 μs to 10 μs.

According to an embodiment, the semiconductor body includes a drift zoneof a first conductivity type. Doping the part of the semiconductor bodyby plasma doping includes doping the part of the semiconductor body withdopants of a second conductivity type complementary to the firstconductivity type. According to one embodiment, the doped part of thesemiconductor body constitutes a charge compensation region, e.g. ap-doped column between an n-doped drift zone of a superjunctionsemiconductor device. According to another embodiment, a transistor ordiode device is formed as the semiconductor device and includes thedoped part of the semiconductor body as a vertical edge terminationstructure. According to an embodiment, the semiconductor device is apower semiconductor device including a breakdown voltage or voltageblocking capability of at least 100 V or at least 300 V.

According to an embodiment, further to plasma doping of the part of thesemiconductor at the sidewalls, a variation of doping along the verticaldirection in a silicon semiconductor body may be achieved by high energyimplantation of protons for n-doping or helium for p-doping. This allowsto improve an avalanche ruggedness of the device.

Further process steps for manufacturing semiconductor zones, e.g.source, drain, body, highly doped contact zones, and gate structures,trench fillings, dielectric layers, interlevel dielectrics, conductivelayers such as highly doped semiconductor layer(s) or metal layer(s) mayfollow to complete the semiconductor device.

FIGS. 2A to 2F illustrate schematic cross-sectional views of an n⁻-dopedsemiconductor body 210 at different phases of processing a semiconductordevice. A mask 212 is formed on a first side 214 of the semiconductorbody 210. Patterning of the mask 212, e.g. by lithography, results inmask openings. A trench 216 is formed from the first side 214 into thesemiconductor body 210, e.g. by using an anisotropic etch process suchas RIE.

As an example, a width w of the trench 216 may range between 0.1 μm to15 μm or between 1 μm to 10 μm. A depth d of the trench 216 may rangebetween 10 μm to 120 μm or between 20 μm to 60 μm. As an example, thedepth d may be appropriately chosen with regard to a desired voltageblocking capability of the semiconductor device to be manufactured.

Referring to the schematic cross-sectional view of the semiconductorbody 210 illustrated in FIG. 2B, plasma doping by PLAD or Pill using aprocess gas configured for p-doping, e.g. BF₃ and/or B₂H₆ is carriedout. Plasma doping leads to p-doping of a part 218 of the semiconductorbody 210 at sidewalls 220 a, 220 b as well as at a bottom side 222 ofthe trench 216 (FIG. 2C). A penetration depth of the dopants, or, inother words, a thickness of the part 218 after PLAD is comparativelylow, e.g. in a range between 0.2 nm and 20 nm, or between 0.5 nm to 10nm or even between 1 nm to 3 nm since comparatively low voltages in therange of 100 V to 12 kV are used in PLAD to accelerate ions towards thesemiconductor substrate. As regards further parameter of plasma doping,reference is drawn to FIG. 1 and the related part of the description.

Referring to the schematic cross-sectional view of the semiconductorbody 210 illustrated in FIG. 2D, the mask 212 is removed from the firstside 214, e.g. by an etch process. Further, an optional outdiffusionbarrier layer 224 is formed on the sidewalls 220 a, 220 b and on thebottom side 222 of the trench 216. The optional outdiffusion barrierlayer 224 lines the p-doped part 218 of the semiconductor body 210. Theoutdiffusion barrier layer 224 counteracts or avoids outdiffusion of thep-type dopants introduced into the part 218 by plasma doping. Thisallows to keep the implanted dose within the semiconductor body 210. Inother words, the outdiffusion barrier layer 224 allows to improve anaccuracy of charge compensation in a superjunction device. As anexample, the outdiffusion barrier layer 224 may be formed as a siliconlayer by CVD at low temperatures, e.g. at temperatures in the range of300° C. and 700° C. or in a range of 400° C. to 600° C. According toanother embodiment, the outdiffusion barrier layer 224 may be formed bydeposition of an amorphous silicon layer followed by crystallizing theamorphous silicon layer at temperatures ranging typically between 400°C. and 600° C. As an alternative or in addition, the outdiffusionbarrier layer 224 may consist of or include an insulating layer, e.g. anoxide layer formed by CVD or plasma enhanced CVD (PECVD). In theembodiment illustrated in FIGS. 2A to 2F, the part 218 covers the bottomside 222 of the trench 216. According to another embodiment, the part218 may be removed from the bottom side 222 of the trench 216, e.g. byan etch process. According to yet another embodiment, the part 218covering the bottom side 222 of the trench 216 may be counter dopedleading to an n-doping at the bottom side 222. Diffusion of the p-typedopants introduced by plasma doping is carried out by thermal heating towiden a profile after PLAD or PIII which is comparatively small due tothe low penetration depth of the dopants achieved by these methods.

The outdiffusion barrier layer 224 and/or an optional insulating layeras part of the outdiffusion barrier layer 224 may be removed afterdiffusion, e.g. by an etch process, But in case of the deposition ofsilicon this is typically not necessary.

Referring to the schematic cross-sectional view of the semiconductorbody 210 illustrated in FIG. 2E, the trench 216 is at least partlyfilled up with an insulating material, e.g. an oxide or nitride, and/ora semiconductor material, e.g. an epitaxial silicon layer formed bylateral epitaxial processes or by CVD. Thus, a filling material 226fills up the trench 216. In case of filling up the trench 216 withsemiconductor material, the semiconductor material may be undoped or maytypically include a doping concentration below the doping concentrationintroduced by the above-described plasma doping of the p-doped part 218or may include a doping concentration which is similar to the doping ofthe semiconductor body 210 so that it can contribute to a current flowwith low resistance.

According to an embodiment, thermal heating is carried out to furtherwiden a lateral doping profile of the p-doped part 218.

Referring to the schematic cross-sectional view of the semiconductorbody 210 illustrated in FIG. 2F, further processes for manufacturing asuperjunction semiconductor device are illustrated. A p-doped bodyregion 228 is formed at the first side 214, e.g. by ion implantation ofp-type dopants such as boron (B). Further, an n⁺-doped source zone 230is formed in the p-doped body region 228 at the first side 214, e.g. byion implantation of n-type dopants such as phosphor (P), Further, aplanar gate structure 232 including a gate dielectric 234 and a gateelectrode 236 is formed at the first side 214. Additional known elementssuch as a drain at a second side opposite to the first side 214,dielectric layers such as interlayer dielectrics and conductive layerssuch as metallization layers which may be interconnected or connected tothe semiconductor body by contacts may follow to complete thesuperjunction device. In the exemplary device illustrated in FIG. 2F,the part 218 constitutes a charge compensation region of a superjunctiondevice. According to other embodiments, the trench 216 and the part 218may constitute a vertical edge termination structure in an edge areatermination area surrounding an active cell area of a transistor device,e.g. an IGBT or MOSFET.

FIGS, 3A to 3F illustrate schematic cross-sectional views of an n⁻-dopedsemiconductor body 310 at different phases of processing a superjunctionsemiconductor device. A mask 312 is formed on a first side 314 of thesemiconductor body 310. Patterning of the mask 312, e.g. by lithography,results in mask openings. Trenches 316 are formed from the first side314 into the semiconductor body 310, e.g. by using an anisotropic etchprocess such as RE.

Dimensions of the trenches 316, e.g. a width w and a depth d, may bechosen as described with regard to the embodiment illustrated in FIGS.2A to 2F. A pitch p between a middle of neighboring trenches 316 mayrange between 0.2 μm and 50 μm or between 0.5 μm to 30 μm or evenbetween 1 μm to 5 μm. Plasma doping by PLAD or Pill using a process gasconfigured for n-doping, e.g. PF₃ and/or PH₃ is carried out, Plasmadoping leads to n-doping of a part 318 of the semiconductor body 310 atsidewalls 320 a, 320 b as well as at a bottom side 322 of the trenches316 (FIG. 3B). A penetration depth of the dopants, or, in other words, athickness of the part 318 after PLAD is comparatively low, e.g. in arange between 0.2 nm and 20 nm, or between 05 nm to 10 nm or evenbetween 1 nm to 3 nm since comparatively low voltages in the range of100 V to 12 kV are used in PLAD to accelerate ions towards thesemiconductor substrate. As regards further parameter of plasma doping,reference is drawn to FIG. 1 and the related part of the description.According to an embodiment, a dose of dopants introduced by plasmadoping via a unit area of the sidewalls 320 a, 320 b is at least fivetimes larger or even ten or twenty times larger than a dose of dopantsin a part of the semiconductor body 310 between the trenches 316 whichcorresponds to (p−w)/2×N, wherein N is a net doping of the n⁻-dopedsemiconductor body 310 between the trenches 316. Further, the mask 312is removed from the first side 314, e.g. by an etch process.

Referring to the schematic cross-sectional view of the semiconductorbody 310 illustrated in FIG. 3C, a first semiconductor layer 340, e.g. aconformal undoped or lightly doped silicon layer is formed on the part318 in the trenches 316 by lateral epitaxy or CVD. As an example, alateral epitaxial process or low pressure CVD (LPCVD) may be used toachieve a conformal deposition of the first semiconductor layer 340lining the sidewalls 320 a, 320 b and the bottom side 322 of thetrenches 316. As an example, a thickness of the first semiconductorlayer 340 may range between 5% and 30% or between 10% and 20% of thewidth w.

Referring to the schematic cross-sectional view of the semiconductorbody 310 illustrated in FIG, 3D, plasma doping by PLAD or PIII using aprocess gas configured for p-doping, e.g. BF₃ and/or B₂H₆ is carriedout. Plasma doping leads to p-doping of the first semiconductor layer340. A penetration depth of the dopants, or, in other words, a thicknessof a doped part 342 of the first semiconductor layer 340 after PLAD iscomparatively low, e.g. in a range between 0.2 nm and 20 nm, or between0.5 nm to 10 nm or even between 1 nm to 3 nm (FIG. 3E). As regardsfurther parameter of plasma doping, reference is drawn to FIG. 1 and therelated part of the description. According to an embodiment, a dose ofdopants introduced by plasma doping via a unit area of the sidewalls 320a, 320 b deviates by less 10%, or less than 5% or even less than 3% fromthe dose of dopants previously introduced into the part 318 by plasmadoping.

Further referring to the schematic cross-sectional view of thesemiconductor body 310 illustrated in FIG. 3E, the trenches 316 arefilled up with an insulating material, e.g. an oxide or nitride, and/ora semiconductor material, e.g. an epitaxial silicon layer formed bylateral epitaxy or CVD. Thus, a filling material 326 fills up thetrenches 316. In case of filling up the trenches 316 with semiconductormaterial, the semiconductor material may be undoped or may include adoping concentration below the doping concentration introduced by theabove-described plasma doping of the n-doped part 318 or p-doped firstsemiconductor layer 340.

Between plasma doping of the first semiconductor layer 340 and fillingup the trenches 316, an outdiffusion barrier layer as illustrated inFIG. 2D may be formed on the first semiconductor layer 340 followed bythermal heating for widening lateral profiles of p-doping and n-dopingin the parts 318, 342, respectively. Optionally a mask againstoutdiffusion can also be deposited directly after the first plasmadoping process with a subsequent high-temperature step and an optionalremoval of this mask.

Referring to the schematic cross-sectional view of the semiconductorbody 310 illustrated in FIG. 3F, the semiconductor body 310 isplanarized at the first side 340, e.g. by chemical mechanical polishing(CMP) and/or by a plasma etch back. Thereby, the first semiconductorlayer 340 is removed fro the first side 314.

Further processes for manufacturing a superjunction semiconductor devicefollow. For further details in this regard, reference is drawn to FIG.2F and the related part of the specification.

FIG. 3G is a schematic illustration of profiles of p-doping and n-dopingalong a line A-A′ of FIG. 3F.

A lateral width of the profiles depends upon a thermal budget leading toa widening of the profiles by diffusion. A doping profile N of a speciesof n-dopants declines from a maximum Nmax in the part 318 to a minimumdoping plateau Nmin in a drift zone being part of the semiconductor body310 between the trenches 316. A value of the doping at the maximum Nmaxis at least a factor of ten or a factor of twenty larger than the dopingat the minimum plateau Nmin. Depending upon a degree of a lateralextension of the profile N. the minimum plateau may be a minimum. Adoping profile P of a species of p-dopants has a maximum Pmax in the pad342.

FIGS. 4A to 4J illustrate schematic cross-sectional views of an n⁻-dopedsemiconductor body 410 at different phases of processing a superjunctionsemiconductor device. A mask 412 is formed on a first side 414 of thesemiconductor body 410. Patterning of the mask 412, e.g. by lithography,results in mask openings. Trenches 416 are formed from the first side414 into the semiconductor body 410, e.g. by using an anisotropic etchprocess such as RIE.

Dimensions of the trenches 416, e.g. a width w and a depth d, may bechosen as described with regard to the embodiment illustrated in FIGS.2A to 2F.

Plasma doping by PLAD or PIII using a process gas configured forn-doping, e.g. PF₃ and/or PH₃ is carried out. Plasma doping leads ton-doping of a pad 418 of the semiconductor body 410 at sidewalls 420 a,420 b as well as at a bottom side 422 of the trenches 416 (FIG. 4B). Apenetration depth of the dopants, or, in other words, a thickness of thepart 418 after PLAD is comparatively low, e.g. in a range between 0.2 nmand 20 nm, or between 0.5 nm to 10 nm or even between 1 nm to 3 nm. Asregards further parameters of plasma doping, reference is drawn to FIG.1 and the related part of the description. According to an embodiment, adose of dopants introduced by plasma doping via a unit area of thesidewalls 420 a, 420 b is at least five times larger than a dose ofdopants in a part of the semiconductor body 410 between the trenches 416which corresponds to (p−w)/2×N, wherein N is a net doping of then⁻-doped semiconductor body 410 between the trenches 416. Further, themask 412 is removed from the first side 414, e.g. by an etch process.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4C, a first semiconductor layer 440, e.g. aconformal undoped or lightly doped silicon layer is formed on the part418 in the trenches 416 by lateral epitaxy or CVD, As an example,lateral epitaxy or low pressure CVD (LPCVD) may be used to achieve aconformal deposition of the first semiconductor layer 440 lining thesidewalls 420 a, 420 b and the bottom side 422 of the trenches 416. Asan example, a thickness of the first semiconductor layer 440 may rangebetween 2% to 30% or between 5% and 20% of the width w.

Referring to the schematic cross-sectional vie of the semiconductor body410 illustrated in FIG. 4D, plasma doping by PLAD or PHI using a processgas configured for p-doping, e.g. BF₃ and/or B₂H₆ is carried out. Plasmadoping leads to p-doping of the first semiconductor layer 440. Apenetration depth of the dopants, or, in other words, a thickness of adoped part 442 of the first semiconductor layer 440 after PLAD iscomparatively low, e.g. in a range between 0.2 nm and 20 nm, or between0.5 nm and 10 nm or even between 1 nm and 3 nm. As regards furtherparameters of plasma doping, reference is drawn to FIG. 1 and therelated part of the description. Furthermore, masking layers preventingoutdiffusion can be formed as described above. According to anembodiment, a dose of p-dopants introduced by plasma doping into a unitarea of the part 442 ranges between 170% and 230%, or between 190% and210%, or between 195% and 205% of the dose of n-dopants previouslyintroduced into the part 418 by plasma doping.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4E, the first semiconductor layer 440 isremoved from the first side 414 and from the bottom side 422 of thetrenches 416, e.g. by an anisotropic etch process. A secondsemiconductor layer 450, e.g. a conformal undoped or lightly dopedsilicon layer is formed on the doped part 442 in the trenches 416, onthe bottom side 422 and on the first side 414 by lateral eptitaxy or byCVD. As an example, lateral epitaxy or low pressure CVD (LPCVD) may beused to achieve a conformal deposition of the second semiconductor layer450 lining the sidewalls 420 a, 420 b and the bottom side 422 of thetrenches 416.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4F, plasma doping by PLAD or PIII using aprocess gas configured for n-doping, e.g. e.g. PF₃ and/or PH₃ is carriedout. Plasma doping leads to n-doping of the second semiconductor layer450. A penetration depth of the dopants, or, in other words, a thicknessof a doped part 452 of the second semiconductor layer 450 after PLAD iscomparatively low, e.g. in a range between 0.2 nm and 20 nm, or between0.5 nm and 10 nm or even between 1 nm and 3 nm. As regards furtherparameters of plasma doping, reference is drawn to FIG. 1 and therelated part of the description. According to an embodiment, a dose ofdopants introduced into the part 452 by plasma doping via a unit area ofthe sidewalls 420 a, 420 b corresponds to the dose introduced into thepart 418 by plasma doping.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4G, the second semiconductor layer 450 isremoved from the first side 414 and from the bottom side 422 of thetrenches 416, e.g. by an anisotropic etch process.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4H, the trenches 416 are filled up with asemiconductor material, e.g. an epitaxial silicon layer formed bylateral epitaxy or CVD. Thus, a filling material 466 fills up thetrenches 416. The semiconductor material may be undoped or may include adoping concentration below the doping concentration introduced by theabove-described plasma doping into the n-doped part 452.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4I, the semiconductor body 410 isplanarized at the first side 440, e.g. by chemical mechanical polishing(CMP) and/or by a plasma etch back. Thereby, the filling material 466 isremoved from the first side 414.

Referring to the schematic cross-sectional view of the semiconductorbody 410 illustrated in FIG. 4J, further processes for manufacturing asuperjunction semiconductor device are illustrated. A p-doped bodyregion 428 is formed at the first side 414, e.g. by ion implantation ofp-type dopants such as boron (B). Further, an n⁺-doped source zone 430is formed in the p-doped body region 428 at the first side 414, e.g. byion implantation of n-type dopants such as phosphor (P). Further, aplanar gate structure 432 including a gate dielectric 434 and a gateelectrode 436 is formed at the first side 414. A drain contact 438 isformed at a second side 472 opposite the first side 414, Additionalknown elements such as dielectric layers, e.g. interlayer dielectricsand conductive layers such as metallization layers which may beinterconnected or connected to the semiconductor body by contacts mayfollow to complete the superjunction device.

The n-dose introduced into the part 418 as illustrated in FIGS, 4A, 4Bdefines an n-doping in drift zone parts 481 a, 481 b and 481 c, Thep-dose introduced into the part 442 as illustrated in FIG. 4D defines ap-doping in charge compensation regions 482 a, 482 b, 482 c, 482 d. Then-dose introduced into the part 452 as illustrated in FIG. 4F defines ann-doping in drift zone parts 483 a, 483 b.

The above described embodiments allow to manufacture superjunctiondevices having a precise charge compensation and compact design withhomogeneous trench sidewall doping.

Terms such as “first”, “second”, and the like, are used to describevarious structures, elements, regions, sections, etc. and are notintended to he limiting. Like terms refer to like elements throughoutthe description.

The terms “having”, “containing”, “including”, “comprising” and the likeare open and the terms indicate the presence of stated elements orfeatures, but not preclude additional elements or features. The articles“a”, an and the are intended to include the plural as well as thesingular, unless the context clearly indicates otherwise.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may hesubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method of manufacturing a semiconductor device,the method comprising: forming a superjunction field effect transistorby: forming trenches in a semiconductor body from a first side; formingcharge compensation layers by doping parts of the semiconductor body viasidewalls of the trenches by introducing dopants by plasma doping; afterforming the charge compensation layers, widening a profile of thedopants introduced by plasma doping by diffusion caused by a thermalheating process; and forming a drain contact at a second side oppositeto the first side, wherein a surface concentration of the dopantsintroduced by plasma doping via a unit area of the sidewalls is at leastfive times larger than a concentration of dopants in a mesa region ofthe semiconductor body between neighboring trenches which corresponds toN, wherein N is a net doping of the semiconductor body between theneighboring trenches.
 2. The method of claim 1, wherein thesemiconductor body is a silicon semiconductor body.
 3. The method ofclaim 1, wherein the semiconductor body is a silicon carbidesemiconductor body.
 4. The method of claim 1, wherein doping parts ofthe semiconductor body by plasma doping comprises adjusting a DC-voltagepulse distance in a range of 100 μs to 10 ms.
 5. The method of claim 1,wherein doping parts of the semiconductor body by plasma dopingcomprises adjusting a DC-voltage pulse width in a range of 0.5 μs to 20μs.
 6. The method of claim 1, further comprising filling the trencheswith an insulating material.
 7. The method of claim 1, furthercomprising filling the trenches with a semiconductor material.
 8. Themethod of claim 1, further comprising forming a first semiconductorlayer on the doped parts of the semiconductor body.
 9. The method ofclaim 8, wherein forming the first semiconductor layer on the dopedparts of the semiconductor body comprises forming a silicon layer bylateral epitaxy or low-temperature chemical vapor deposition.
 10. Themethod of claim 8, wherein forming the first semiconductor layer on thedoped parts of the semiconductor body comprises: forming an amorphoussilicon layer on the doped parts of the semiconductor body: andcrystallizing the amorphous silicon layer by a heat treatment.
 11. Themethod of claim 1, further comprising forming an outdiffusion barrierlayer on the sidewalls of the trenches.
 12. The method of claim 1,wherein the semiconductor body includes a drift zone of a firstconductivity type, and wherein doping parts of the semiconductor body byplasma doping comprises doping the parts of the semiconductor body withdopants of a second conductivity type complementary to the firstconductivity type.
 13. The method of claim 1, wherein the semiconductorbody includes a drift zone of a first conductivity type, and whereindoping parts of the semiconductor body by plasma doping comprises dopingthe parts of the semiconductor body with dopants of the firstconductivity type, the method further comprising: forming a firstsemiconductor layer over the parts of the semiconductor body in thetrenches; and doping the first semiconductor layer by plasma doping withdopants of a second conductivity type complementary to the firstconductivity type.
 14. The method of claim 13, further comprising:removing the first semiconductor layer from a bottom side of thetrenches; forming a second semiconductor layer over the firstsemiconductor layer in the trenches; and doping the second semiconductorlayer by plasma doping with dopants of the first conductivity type. 15.The method of claim 1, further comprising forming body regions in thesemiconductor body at the first side, the body regions overlapping thecharge compensation layers.
 16. A method of manufacturing asemiconductor device, the method comprising: forming trenches in asemiconductor body from a first side: doping parts of the semiconductorbody via sidewalls of the trenches by introducing dopants by plasmadoping; and after introducing the dopants by plasma doping, widening aprofile of the dopants introduced by plasma doping by diffusion causedby a thermal heating process, wherein a surface concentration of thedopants introduced by plasma doping via a unit area of the sidewalls isat least five times larger than a concentration of dopants in a mesaregion of the semiconductor body between neighboring trenches whichcorresponds to N, wherein N is a net doping of the semiconductor bodybetween the neighboring trenches.
 17. The method of claim 16, whereinthe semiconductor body includes a drift zone of a first conductivitytype, and wherein doping parts of the semiconductor body by plasmadoping comprises doping the parts of the semiconductor body with dopantsof a second conductivity type complementary to the first conductivitytype.
 18. The method of claim 16, wherein the semiconductor bodyincludes a drift zone of a first conductivity type, and wherein dopingparts of the semiconductor body by plasma doping comprises doping theparts of the semiconductor body with dopants of the first conductivitytype, the method further comprising: forming a first semiconductor layerover the parts of the semiconductor body in the trenches; and doping thefirst semiconductor layer by plasma doping with dopants of a secondconductivity type complementary to the first conductivity type.
 19. Themethod of claim 18, further comprising: removing the first semiconductorlayer from a bottom side of the trenches; forming a second semiconductorlayer over the first semiconductor layer in the trenches; and doping thesecond semiconductor layer by plasma doping with dopants of the firstconductivity type.
 20. The method of claim 16, wherein the semiconductorbody is a silicon carbide semiconductor body.